this invention relates to a voice control system wherein the presence of a noise component received concurrently with a voice signal is detected for determining the S/N ratio thereby the circuit condition of a telephone or other communication system.
In a prior art hand free telephone set utilizing a voice control circuit, the switching between voice transmitting and receiving states is effected by detecting the presence of a received voice signal. Generally, however, since noise components such as peripheral noise and line noise are also received together with the voice signal, misoperation of the voice control circuit has been inevitable.
To eliminate the noise components various solutions have been proposed including a method of utilizing a directive microphone which utilizes the directivity of voice, and a method in which a plurality of microphones are used to detect the difference in the input signals to the microphones for eliminating the peripheral noise by utilizing acoustic coupling. Further, according to an electrical method, filters are used to eliminate the noise components for discriminating the voice input from the noise input thus elevating the switching level of the voice input. However, a simple and effective method has not been proposed. More particularly, in the acoustic method highly trained skill is necessary whereas in the electrical method the level at which the commencement of the voice is detected is limited so that the differences in personal ability results in instability of operation and delay in switching time. As a result, smooth operation was not obtained.
Such methods of solving the problem are not effective because they involve difficult engineering problems and are expensive.